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copied!<p>Ok, best effort, Scala 2.8. We need to reconstruct attributes, which means we have to decompose them correctly. Let's create a function for that:</p> <pre><code>import scala.xml._ case class GenAttr(pre: Option[String], key: String, value: Seq[Node], next: MetaData) { def toMetaData = Attribute(pre, key, value, next) } def decomposeMetaData(m: MetaData): Option[GenAttr] = m match { case Null => None case PrefixedAttribute(pre, key, value, next) => Some(GenAttr(Some(pre), key, value, next)) case UnprefixedAttribute(key, value, next) => Some(GenAttr(None, key, value, next)) } </code></pre> <p>Next, let's decompose the chained attributes into a sequence:</p> <pre><code>def unchainMetaData(m: MetaData): Iterable[GenAttr] = m flatMap (decomposeMetaData) </code></pre> <p>At this point, we can easily manipulate this list:</p> <pre><code>def doubleValues(l: Iterable[GenAttr]) = l map { case g @ GenAttr(_, _, Text(v), _) if v matches "\\d+" => g.copy(value = Text(v.toInt * 2 toString)) case other => other } </code></pre> <p>Now, chain it back again:</p> <pre><code>def chainMetaData(l: Iterable[GenAttr]): MetaData = l match { case Nil => Null case head :: tail => head.copy(next = chainMetaData(tail)).toMetaData } </code></pre> <p>Now, we only have to create a function to take care of these things:</p> <pre><code>def mapMetaData(m: MetaData)(f: GenAttr => GenAttr): MetaData = chainMetaData(unchainMetaData(m).map(f)) </code></pre> <p>So we can use it like this:</p> <pre><code>import scala.xml.transform._ val attribs = Set("attr1", "attr2") val rr = new RewriteRule { override def transform(n: Node): Seq[Node] = (n match { case e: Elem => e.copy(attributes = mapMetaData(e.attributes) { case g @ GenAttr(_, key, Text(v), _) if attribs contains key => g.copy(value = Text(v.toInt * 2 toString)) case other => other }) case other => other }).toSeq } val rt = new RuleTransformer(rr) </code></pre> <p>Which finally let you do the translation you wanted:</p> <pre><code>rt.transform(<a><b attr1="100" attr2="50"></b></a>) </code></pre> <p>All of this could be simplified if:</p> <ul> <li>Attribute actually defined prefix, key and value, with an optional prefix</li> <li>Attribute was a sequence, not a chain</li> <li>Attribute had a map, mapKeys, mapValues</li> <li>Elem had a mapAttribute</li> </ul>

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